The present invention relates to a gas, that is, a cleaning or etching gas, for removing deposits by a gas-solid reaction and a removal method using the gas.
In thin-film device production process of semiconductor industry, optical device production process, super steel material production process and the like, various thin films, thick films, powders, whiskers and the like are produced, for example, by chemical vapor deposition, (CVD), physical vapor deposition (PVD), sputtering, and sol-gel process. During the production of these materials, unnecessary deposits in the form of film, whisker or powder are inevitably formed, for example, on a reactor's inner wall and a jig for supporting the object, as well as on the object. This may cause the occurrence of unnecessary particles, making it difficult to produce films, powders, whiskers and the like of good quality. Thus, it becomes necessary to occasionally remove the unnecessary deposits, for example, by cleaning gas. Such a cleaning gas is required, for example, to have (1) a high reaction rate at which the cleaning gas reacts with unnecessary deposits to form volatile compounds, (2) a relative easiness to make the exhaust gas of the cleaning unharmful, and (3) a relative unstableness in the atmosphere to make the impact on the global warming smaller. Conventional examples of the cleaning gas are C2F6, CF4, C4F8, NF3 and ClF3. These compounds, however, have the following defects. Firstly, ClF3 is highly reactive, and thus may do damage to materials conventionally used for the apparatus, when ClF3 is used at a high temperature or with the assistance of plasma. Secondly, NF3 is low in reactivity unless the reaction temperature is at least 300° C., and thus may be impossible to remove unnecessary deposits accumulated in the piping of the apparatus and the outside of the plasma region. Furthermore, it is necessary to have a high temperature in order to make the exhaust gas unharmful. Thus, the cost for conducting the cleaning becomes relatively high. Thirdly, each of C2F6, CF4 and C4F8 has the following defects. That is, it may be impossible to remove unnecessary deposits accumulated in the piping of the apparatus and the outside of the plasma region. Furthermore, a fluorocarbon(s) will accumulate by the plasma cleaning. If oxygen is added in order to decrease the amount of the accumulation of the fluorocarbon(s), an oxide(s) will accumulate instead. Since each of C2F6, CF4 and C4F8 is a very stable compound, it is difficult to treat the exhaust gas of the cleaning. In other words, these compounds (gases) will be stably present in the environment, and cause adverse impact against the environment due to their high global warming coefficients or factors. Thus, it is necessary to have a high temperature for the treatment of the exhaust gas. This makes the cost of the treatment relatively high.
An etching gas, which is analogous to the above-mentioned cleaning gas, is used for partially removing a thin film material in order to transfer the circuit pattern, for example, of LSI and TFT. Conventional examples of this etching gas are CF4, C2F6, CHF3, SF6, and NF3. These gases have a problem of high global warming coefficient. Furthermore, these gases are relatively stable gases. Thus, it is necessary to use a large amount of energy for generating, for example, CF3 radicals and F radicals, which are useful as etchant. That is, the electric power consumption becomes large. Furthermore, it is relatively difficult to treat the unreacted etching gases, prior to the discharge into the atmosphere. Therefore, there is an urgent demand for an alternative etching gas(es) that can easily be made unharmful on the global environment and is capable of achieving high precision etching.